When cement slurry is displacing down into a well casing and out into the annular space between such casing and a surrounding well casing, it is imperative that the cement completely fill such annulus. Unless this occurs, there can be channels that form in the cement before it hardens, and through which formation fluids, such as salt water, can migrate so that a complete shut off is not achieved. Where channels are present, it is necessary to recement the casing with the objective of closing off such channels. A complete shut off is particularly important where a well is being plugged and abandoned.
Applicant has found that better cementing results can be obtained if the inner casing string is perforated in a manner such that a plurality of angularly spaced, vertical series of holes are formed that allow circulation of cement through such holes and into the annulus outside. This process provides a uniform distribution of a large number of small, individual cement flow paths, and prevents the formation of channels in the annulus. In accordance with a further aspect of the present invention, the shaped charges are arranged to form holes in the inner casing string without damaging an outer string of casing that surrounds such inner casing string. The shaped charges are arranged within carriers that are pressed against the casing wall by bias means, and in such a manner that any debris remains within the carriers, and no trash is left in the well.
A general object of the present invention is to provide a new and improved casing perforating apparatus for forming circulation paths through the wall of a casing.
Another object of the present invention is to provide a new and improved perforating gun that forms a plurality of evenly distributed flow paths in the wall of a casing so that cement can be placed behind the casing without formation of channels.